Field of the Invention
The present disclosure relates to an image reading apparatus and an image forming apparatus and more specifically to a configuration for preventing deterioration of reading accuracy of an image reading portion over time.
Description of the Related Art
Hitherto, an image reading apparatus such as an image scanner is configured to read an image of a document in a condition being placed on a platen glass as a transparent member. Still further, a conventional image forming apparatus such as a digital copier and a printer includes an image forming portion and an image reading apparatus and is configured to form an image onto a sheet by the image forming portion based on image information read by the image reading apparatus.
The image reading apparatus includes an image reading portion including a light source movably in a sub-scan direction. Then, in reading the image of the document, the image reading apparatus moves the image reading portion in the sub-scan direction, irradiates the document with light from the light source and detects reflection light from the document.
As such an image reading apparatus, there is one provided with a resin-made guide shaft and a rail integrated with a resin-made casing and configured to move the image reading portion along the guide shaft and the rail in reading an image as disclosed in Japanese Patent Application Laid-open No. 2014-3396 for example.
By the way, in the image reading apparatus as disclosed in Japanese Patent Application Laid-open No. 2014-3396, the image reading portion located at a reading starting position is moved to an image reading ending position in reading the image, and then the image reading portion which has moved to the image reading ending position is returned to the reading starting position after ending to read the image. That is, in the image reading apparatus described above, the image reading portion reciprocates between the reading starting position and the image reading ending position along the resin-made guide shaft and the rail in reading the image.
However, in the case of the configuration in which the image reading portion is moved along the guide shaft and the rail, parts of the resin-made guide shaft and rail corresponding to a moving range of the image reading portion causes wear over time. For instance, in a case where a document whose size is smaller than a maximum size document that can be read by the image reading apparatus is read repeatedly, a moving range of the guide shaft and the rail between the reading starting position and the image reading ending position corresponding to the small size document causes wear.
If the guide shaft and the rail wear over time as described above, a difference in level is generated at the image reading ending position of the guide shaft and the rail corresponding to the small size document, i.e., at the position where the image reading portion stops. Here, because a distance between the reading starting position and the image reading ending position corresponding to a large size document is longer than that of the small size document, the image reading portion passes through the image reading ending position of the small size document until when the image reading portion arrives at the image reading ending position in reading the large size document image. If the difference in level is generated at the image reading ending position corresponding to the small size document, the image reading portion hits against the difference in level, and the document image reading accuracy of the image reading portion deteriorates due to an impact.